Manganese-base alloy and method of making and using the same



Patented June 24, 1941 MAN GANESE-BASE ALLOY AND METHOD OF MAKING ANDUSING THE SAME William Kroll, Luxemburg, Luxcmburg -No Drawing. Originalapplication January 17,

1940, Serial No. 314,229.

ary 4, 1939.

In Luxemburg, J anu- Divided and this application Jannary 31, 1940,Serial No. 316,543

3 Claims.

The invention relates to alloys containing a large proportion ofmanganese, and has for one of its principal objects the provision ofmanganese alloys which may be cold-worked. Another object is to providea method of making and treating such alloys to improve their amenabilityto cold-working.

It is known that electrolytically refined gamma manganese remains inthat state for several weeks, and that during such time it may becoldworked. But in time the gamma manganese alters to the brittle alphaform, and it has heretofore been impossible to obtain by thermaltreatment forms of manganese or high-manganese alloys that are stablyductile at room temperatures.

I have observed that pure manganese obtained by distillation may be hotrolled at temperatures above the alpha-betatransformation point, thebest results being obtained in the neighborhood of the gammatransformation point; but when quenched it-pass'es over immediately tothe brittle alpha state.

The present invention is based on the discovery that the above-describedconversion of ductile manganese to the brittle form may be to a greatextent prevented by means of certain alloying additions which act toinhibit such conversion, and that when suitable thermal treat ment isemployed, the resulting alloys may be kept in a ductile condition atroom temperature.

The alloying addition producing the most favorable results is copper ina proportion of about 1% to 60%, preferably between 10% and 35%, of thealloy.

In order to obtain the maximum freedom from brittleness, it is importantwhen making the alloys to protect the molten metal from the nitrogen andoxygen of the air. This may be done by the use of protective fluxes, e.g. slags containing manganese chloride, manganese oxide .structure isstill present, cooling to room temperatureand reheating to rollingtemperature will cause cracks and red-shortness.

According to the invention, the cast ingots, still hot, are hot rolledinthe gamma-beta regions until the grain has been broken down. The l5thinner cross sections may then be rapidly cooled,

thereby avoiding embrittlement. Thus, for example, ingots .50 mm. of amanganese alloy containing 15% or more copper are rolled at 950 G. intosheets 2 mm. thick which may then be air cooled.

Cold working may be done within wide limits. intermediate anneals beingeffected by rapid heating to within the beta or gamma field, followed byquenching.

Although the manganese-copper alloys are relatively stable, theynevertheless tend to become brittle when heated to certain moderately.

nese alloy becomes brittle in the same time at 500 C. The iron, 65%manganese alloy can stand up to 450 C. The transformation and alkalineearth metal halides; or by the use of a protective atmosphere, forinstance hydrogen, methane, and the rare permanent gases such as argonor helium; or by the use of a partial vacuum, if it be not carried tosuch a point as to vaporize manganese too rapidly; or by a combinationof two or three of these measures. Clay crucibles may be used inpreparing the alloy.

The hot rolling of the alloys of the invention must be conductedentirely aboife the beta-alpha transformation temperature, andpreferably is commenced while the alloy is in the gamma form. Otherwise,the metal tends to be redshort or cold-short. The beta-alpha point iscausing embrittlement requires a certain time at the criticaltemperature, therefore no brittleness appears when the alloy passesrapidly through the critical temperature range, and it is possible so tocontrol the embrittlement as to exploit it for the purpose of increasingthe hardness and strength of the alloy. Thus, a binary manganese-copperalloy containing 15% copper was rolled at 900 C. and quenched. Thetensile strength of the rolled and quenched sheets, 0.75 mm. thick, was40.3 kg./mm. with an elongation of'34.5% and a Brinell hardness of 111.By re- .heating the sheets at 500 C, for five minutes the suitableproportions of nickel and copper, preferably within the range of 0.5% to10% nickel and 5% to 40% copper, the tendency to become embrittled atmoderately elevated temperatures within the alpha field is suppressedand may be substantially eliminated. For example, an alloy containing6.9% Ni, 5.1% Cu, rest Mn, is substantially entirely stable, and afterworking and quenching from 950 C. has a tensile strength of 39.9 ken/mm.with 20% elongation and a Brinell hardness of 105. In general, thealloys containing the higher percentages of copper tolerate the highernickel additions.

Aluminum may be added to the alloys in an amount suitably between 0.1%and (the higher percentages preferably being used with the higher copperpercentages) to deoxidize them, thereby improving their workability.Furthermore, aluminum protects the alloy against oxidation at hightemperatures, and during melting and casting it forms a superficial filmof oxide which hinders oxidation and nitrogen pick-up. It promotes theexistence of a surface favorable for rolling. The aluminum-5 containingalloys may advantageously be made from manganese produced byalumino-thermic reduction.

Zinc may also be added in a proportion up to 20%, the copper preferablybeing correspondingly reduced. A more narrowly circumscribed limit forsuch alloys is between 5% and 35% copper and 1% to 8% zinc. Forinstance, an alloy containing 10% Cu, 5% Zn, rest Mn, after rolling andquenching from 1050 C. and subsequent cold working, had a tensilestrength of 47.7 kg./mm. with 13.1% elongation and a Brinell hardness of131.

Other metals may be present, as one or more of iron, cobalt, tungsten,or chromium, in 'a total percentage up to 5% but preferably not overabout 2%. In general, the elements Si, Sn, Ti, Ta, Mo, Ag, Ce, Mg, andBe appear to be injurious and should ordinarily not exceed 0.5% Si, 1%Sn, 2% Ti, 5% Ta, 2% Mo, 2% Ag, 2% Ce, Mg, or 0.5% Be. Calcium, lithium,or thorium may be used in a proportion of 1% or more as a deoxidizer.The alloys containing the higher percentages of copper or of copperandnickel will tolerate the higher amounts of such other metals. It ispreferred that the silicon content be less than 0.15%.

Iron in a proportion between 30% and 50% (up to 5% of. which may bereplaced by one or more of the elements nickel, cobalt, tungsten,molybdenum, titanium, and chromium) may be used as the stabilizing metalinstead of the copper; but the stabilizing effects oi iron are not, ingeneral, as strong as those produced by copper. The beta-alpha point isabout 600 to 742 C. in the case of the iron-manganese alloys.

The alloys of the invention preferably contain less than 0.2% carbon andshould usually contain less than 0.05% of this element, althoughsomewhat higher carbon contents will on occasion be permissible. It isalso preferred that the manganese content be at least 50%, although onoccasion it may be as low as 40%.

The resistance of the alloys of the invention to corrosion =by moist airis about the same as thatof pure copper. Scaling accompanied by peelingis noticeable only above 600 C. in the case of the lower copper alloysand only above 700' C. in the case of the higher copper alloys. 1

The alloys containing over 30% copper may easily be soldered with'.either soft or hard solder.

Those with less than 30% copper are soldered with some difllculty.

The alloys of the invention have a particularly high electricalresistivity, generally between about 1.2 and 2 ohm/m./mm. For instance,the binary manganese-copper alloy containing 40% copper has aresistivity slightly more than 2 ohm/m./mm.* The binary alloysage-harden, with a decrease in electrical resistivity. The stablemanganese-copper nickel alloys, are particularly useful as resistancealloys. For example. an alloy containing about 37% copper, 8% nickel,rest manganese, has an electrical resistivity of about 1.8 ohmlmlmmfi,three times that of commercial resistance-wires of copperbase alloys.while an alloy containing 5% copper,

8% nickel, rest manganese, has a resistivity of 1.35 ohm/m./mm.

The highest resistivities are obtained in the range of 30% to copper,and the addition of 6% to 8% nickel is suiiicient to stabilize thealloy. If the alloy is to be used at temperatures below 100 C., thenickel content may be as low as 0.5% or be eliminated entirely. If desired, the nickel content may be raised as high as 20%. Nickel onlyslightly aifects the resistivity, the latter being determined chiefly bythe solid solution of manganese and copper.

Within the range of 25% to 55% copper, 0% to 15% nickel, rest manganese,the temperature coefficient of electrical resistivity is low, e. g.alpha=0.0003 for an alloy containing 50% manganese and 50% copper. Thehigher-manganese alloys have a relatively high temperature coefficient,for instance, -alpha=0.03 for an alloy containing manganese and 5%copper. Nickel does not have any. pronounced effect on the temperaturecoeflicient of electrical resistivity.

The alloys of the invention also have an unusually high coeflicient ofexpansion, and are accordingly useful as thermoregulatorelements. Ifsuch elements are to be used at elevated temperatures, the stableternary. manganese-copper,- nickel alloys containing about 4% to 20%,preferably 5% to 12%, nickel are most suitable.

An alloy containing 5% copper and 8% nickel, rest manganese, has anaverage coeflicient of expansion of alpha=390 10", an electricalresistance of about 1.3 ohm/mJmmF, a Brinellhardness of about 150, and amelting point at about, 1100" C. The temperature-expansion curve isalmost straight, is without breaks, and is reproducible as often asdesired.

An alloy containing 37% copper and 8% nickel, rest manganese has acoefllcient of expansion of alpha-=290X 10- and an electrical resistanceof more than 1.8 ohm/mJmn'i.

Bimetallic elements may be formed by fastening a strip of metal having alow thermal expansion, e. g. an iron-nickel alloy of the Invar type, oran iron-nickel-cobalt alloy of the Kovar" type, of the alloy of theinvention, as by casting, soldering, or welding.

It is to be understood that the several specific compositions describedherein are examples illustrative of the invention, and that theinvention is not limited to or by such examples.

This application is a division of my application Serial Number 314,229,filed January 17, 1940.

I claim:

1. Method of making a wrought article of a manganese-ba e valloycontaining upwards of 40% manganese, which comprises forming a melt fromsubstantially pure manganese and a-minor percentage at least 1% ofcopper which acts to stabilize the gamma phase of manganese, such meltbeing substantially free from embrittling elements; casting andsolidifying the alloy melt; and, before the casting has cooled below thetransformation temperature at about 740 0., hot deforming the casting tobreak down the grain.

2. Method as claimed in claim 1, wherein the hot deformed alloy isthereafter cold rolled in a plurality of stages and annealed betweensuch stages, said annealing being effected by heating the alloy to, andquenching it from, a temperature above the alpha-beta point (about 740C.).

3. Method of making a wrought article of a manganese-base alloy whichcomprises forming a melt from substantially pure manganese and aneffective percentage above 0.5% of an element having the property ofstabilizing the gamma phase of manganese and selected from the groupconsisting of copper, nickel, and iron, such melt being substantiallyfree from embrittling elements and containing upwards of 40% manganese;casting and solidifying the alloy melt; before the casting has cooledbelow the transformation temperature at about 740 C., hot rolling thecasting; and thereafter quenching the casting.

' WILLIAM KROLL.

